The present invention relates to the field of delivery systems and methods for deploying intravascular stents, and more specifically, to delivery systems that incorporate mechanical gripping devices for maintaining self-expanding stents in a compressed state during delivery to facilitate accurate deployment of the stent within the body vessel.
Cardiovascular disease currently takes the lives of almost one million Americans each year. Diseases of the vascular system may occur as a result of several etiologies that lead to the development of atherosclerosis, a disease of the arteries characterized by thickening, loss of elasticity, and calcification of arterial walls, which manifests itself in two predominant forms. In one form, a narrowing of blood vessels impedes blood flow through the vessel lumen. In another form, arterial walls degenerate due to the formation of aneurisms, which cause the walls of the affected artery to weaken and balloon outward while thinning. Although many patients with vascular disease choose to explore treatments that do not require surgery, such as cholesterol reducing regimens or drugs, beta blockers to regulate and reduce blood pressure, and blood-thinning agents, vascular surgery still remains an often performed procedure. In the United States alone, more than 850,000 angioplasties and bypasses are currently performed annually at a cost of around $30 billion.
As a less invasive alternative to bypass surgery, atherectomy has become a widely accepted procedure because it removes built up plaque from the inside of blood vessels that have experienced the progressive occlusive effects of atheroscierosois. Atherectomy is exercised most commonly in major arterial vessels, such as the coronary arteries, and can be accomplished by various means, including lasers, incisions, drill tip catheters. Angioplasty is another non-invasive procedure where a balloon-tipped catheter or other device is used to enlarge a narrowing in a artery. This enlargement is accomplished by radially compressing the atherosclerotic plaque of a stenosis against the inside of the artery wall, and dilating the lumen of the artery.
Although angioplasty procedures are widely accepted for treatment of occluded arteries, the problem of restenosis following an angioplasty treatment is a significant danger that a patient must face. Restenosis is the closure of an artery following trauma caused by attempts to open an occluded portion of the artery, and is frequently caused by the elastic rebound of the arterial wall and/or by dissections in the vessel wall caused by the angioplasty procedure. To combat restenosis, vascular surgeons implant tubular supports known as xe2x80x9cstentsxe2x80x9d into surgically repaired vessels.
Stents are used to support dissections in vessel walls and to prevent the elastic rebound of repaired vessels, thereby reducing the level of restenosis for many patients. The stent is typically inserted by catheter into a vascular lumen at an easily accessible location, such as the brachial or femoral arteries, and then is advanced through the vasculature to the deployment site. The stent is initially maintained in a radially compressed or collapsed state to enable it to be maneuvered through the body lumen. Once in position, the stent is expanded into contact with the diseased portion of the arterial wall, thereby providing internal support for the lumen. One method for expanding the stent at the site of the stenosis employs some active external means to apply a controlled force that expands the stent, such as a balloon in typical balloon angioplasty catheter. Details of prior art expandable stents and their representative associated delivery systems can be found in U.S. Pat. No. 3,868,956 (Alfidi et al.); U.S. Pat. No. 4,512,1338 (Balko et al.); U.S. Pat. No. 4,553,545 (Maass, et al.); U.S. Pat. No. 4,733,665 (Palmaz); U.S. Pat. No. 4,762,128 (Rosenbluth); U.S. Pat. No. 4,800,882 (Gianturco); U.S. Pat. No. 4,886,062 (Wiktor); U.S. Pat. No. 5,514,154 (Lau, et al.); U.S. Pat. No. 5,421,955 (Lau et al.); U.S. Pat. No. 5,603,721 (Lau et al.); U.S. Pat. No. 4,655,772 (Wallsten); U.S. Pat. No. 4,739,762 (Palmaz); U.S. Pat. No. 5,569,295 (Lam); U.S. Pat. No. 5,899,935 (Ding); U.S. Pat. No. 6,007,543 (Ellis et al.); U.S. Pat. No. 6,027,510 (Alt); and U.S. Pat. No. 6,077,273 (Euteneuer et al.).
Another method employed for expansion of a stent at the site of stenosis relies on the removal of some restraint that holds the stent in a compressed state, such as a sheath, a collar, a clamp, or a membrane. For this method to succeed, the stent must be capable of self-expansion when the restraint is removed. Self-expanding stents can be formed from shape memory metals or super-elastic nickel-titanum (NiTi) alloys (nitinol), which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery catheter into blood vessel once its restraining device is removed. Self-expanding stents, manufactured from expandable heat-sensitive materials, allow for phase transformations of the material to occur, resulting in the expansion and contraction of the stent.
Details of prior art self-expanding stents and their representative associated delivery systems can be found in U.S. Pat. No. 4,580,568 (Gianturco); U.S. Pat. No. 4,655,771 (Wallsten); U.S. Pat. No. 4,655,771; U.S. Pat. No. 4,732,152 (Wallsten); U.S. Pat. No. 4,848,343 (Wallsten); U.S. Pat. No. 4,830,003 (Wolff, et al.); U.S. Pat. No. 4,875,480 (Imbert); U.S. Pat. No. 4,913,141 (Hillstead); U.S. Pat. No. 4,950,227 (Savin); U.S. Pat. No. 5,071,407 (Terrain); U.S. Pat. No. 5,064,435 (Porter); U.S. Pat. No. 5,571,135 (Fraser); and U.S. Pat. No. 5,989,280 (Euteneuer et al.).
A need exists in the market place for a self-expanding stent delivery system that is effective to maintain the stent to its low profile state and allow for accurate and reliable placement within the vessel lumen at the deployment site. Such a system also should be easy to maneuver and control for the physician performing the procedure. The surgeon deploying the stent would also benefit if such a system was designed with an adjustment element to allow for quick and accurate alignment of a post-dilatation stent in the event of an inaccurate placement of the stent.
Various attempts have been made to develop delivery systems for self-expanding stents that result in accurate and reliable deployment in the vessel lumen, however, there have been some problems associated with these systems. Many incorporate delivery sheaths to restrain the stent prior to deployment. Such devices typically add to the profile of the stent delivery catheter thereby adding a possible obstacle to placement in a narrow body lumen. Often, the stent itself is not compressed to a small enough diameter to adequately navigate the tortuous vasculature of the anatomy, which can result in damage to vessel walls and inefficient delivery.
Deployment systems for self-expanding stents may also imprecisely deploy the stent due to a failure to compensate for axial energy storage in the stent itself, or frictional forces created by the delivery system. For example, systems that rely on a xe2x80x9cpush-pullxe2x80x9d design can experience movement of the collapsed stent within the body vessel when the sheath and inner catheter are pushed together. Additionally, some self-expanding stents can store energy axially from the frictional force generated as the outer restraining sheath is retracted over the expanding stent. This can cause the stent to act somewhat like a spring, storing energy as the frictional force acts on the stent. As the stent expands beyond the end of the sheath, stored energy can be immediately released, which can cause the stent to xe2x80x9cjumpxe2x80x9d or move from the desired position, resulting in inaccurate placement in the body vessel.
Additionally, some delivery systems fail to provide an element to permit adjustment of the post-dilatation positioning of the stent within the vessel in the event of an imprecise deployment. In these circumstances, surgeons must adjust the positioning of the stent by removing the initial delivery system and inserting a second delivery catheter to reposition the stent. This procedure can be both time consuming and costly to the patient.
Therefore, there is a need for a self-expanding stent delivery system that reliably maintains the collapsed stent in a low delivery profile, facilitates minimal movement of the stent during deployment, results in reliable accurate positioning within the vessel lumen, and incorporates a post-dilatation device for adjusting the stent after deployment if required. The present invention satisfies these and other needs.
The present invention provides a delivery system for a self-expanding stent that maintains the compressed stent in a low delivery profile for navigation of the vasculature and increases the reliability and accuracy of deployment at the target site within the body lumen. Moreover, the present invention overcomes the shortcoming of some traditional restraining delivery systems which require a sheath to maintain the collapsed stent in its delivery position and also reduces the tendency of the stent to release stored energy that may cause it to xe2x80x9cjumpxe2x80x9d in the distal direction, as its proximal end exits the sheath. The present delivery system achieves the above-described advantages by utilizing a mechanically controlled apparatus which contracts the self-expanding stent and secures the stent in a low profile configuration during delivery.
The delivery system of the present invention is characterized by a stent contracting apparatus which coaxially receives the stent and has retractable grippers (also referred to herein as xe2x80x9cgrippersxe2x80x9d) selectively extendable to hook onto the stent and draw the stent radially inwardly into its low profile delivery configuration. The system includes an actuator operable to release the grippers from the stent to free it for expansion. In one aspect of the invention, the actuator is operable to cause the grippers to progressively release the stent, progressing from the distal end of the stent to the proximal end.
In another aspect of the present invention, radial grippers are connected on their inner extremities to longitudinal rails which are shiftable longitudinally in one direction to selectively pivot the grippers to their retracted positions to hook the walls of the stent and to hold it in its compressed delivery profile. The grippers also are shiftable in the opposite direction to unhook their respective free ends from the retained stent to free the stent for expansion within the patient""s vasculature.
In preparation, the stent contracting apparatus may be telescopically advanced into the inner lumen of the expanded stent with the compressed grippers hooked to the struts of the stent to hold the stent. Then, the grippers can be actuated to compress the stent to a low profile for delivery within the patient""s vasculature.
In a particular aspect of the present invention, the radial grippers become progressively shorter in length, from the distal to the proximal end of the stent contracting apparatus, to provide a progressive and controlled release and expansion of the stent from its compressed position to enhance accurate placement within the vasculature.
A post-dilatation expandable balloon may be attached proximal to the stent contracting apparatus to facilitate adjustment of the position of the expanded stent in a post-dilation procedure. The grippers of the stent contracting apparatus may be retracted and the apparatus advanced distally beyond the expanded stent to position the balloon longitudinally within the expanded stent. The balloon may be inflated, as needed, to distend against the stent wall to adjust the stent placement as necessary.
Other objects and features of the invention will become apparent from consideration of the following descriptions, taken in conjunction with the accompanying drawings, which illustrate by way of example the features of the invention.